Manchester United’s already troubled stock market flotation suffered a fresh blow today when a US research team said the shares were worth less than $5 each.

That compares with the $14 at which the shares joined the New York Stock Exchange on Friday, a price that was already lower than the $16-$20 range announced just a few weeks ago.

Amid criticism from football finance experts that the float is “priced to fail”, that the shares pay no dividend and have no hope of doing so, and that football floats in general have a poor history, there were growing suggestions today that the Manchester United deal was overpriced at best.

PrivCo, the Private Company Financial Data Authority, says the business is also being buffeted by the “Facebook effect” as investors increasingly fear that buying into Wall Street will leave them burned.

PrivCo, based in New York, said: “Manchester IPO’s overpricing by some 280% had no reasonable economic basis, as companies and bankers counting on a ‘retail investor put’ in light of the team’s large fanbase to place a floor under the stock’s price failed to materialise.”

The firm says a fair value for the shares is $4.97, a price it could reach within a year.

If PrivCo is right, that would leave the club valued at $800 million (£510 million), rather than the more than $3 billion the owners were hoping for.

The company compared United with other publicly listed football clubs, including Juventus, Roma and Borussia Dortmund, and recent takeovers of other sports clubs or franchises, including Liverpool, LA Dodgers and Boston Celtics, before predicting United will emulate Facebook.

Manchester United has been controlled since 2005 by billionaire US sports investors the Glazer family, who paid £800 million for the club, but have since tried to argue that it is worth much more than this because of its international fanbase.

In the float prospectus, the 134-year-old club said it had an audience of four billion viewers in the 2010-11 season. Much of its future strategy is based on exploiting opportunities outside the UK. It made a profit of £13 million in 2011.

Asked to comment, one City financier and Manchester United fan said: “United is worth £800 million, no more. This ‘float’ will be a good idea if the price drops and these dreadful owners are forced to quit fleecing United for cash.”

Approximately 10% of the shares were sold off, raising $233 million to pay off some of the more than £400 million in debt.